Gas Exchange Flashcards
What happens when a cell increases in size?
• diffusion pathway gets longer
In order to achieve the maximum rate of diffusion, a respiratory surface must be what?
- thin : so diffusion pathways are short
- permable : allow respiratory gases through
- maintain a concentration gradient
- large S.A to volume ratio : to satisfy needs of organism
- moist : allow medium which gases dissolve before diffusion
Name one unicellular organism?
• amoeba
Why is diffusion efficient in amoeba?
- has extremely large S.A : volume ratio
- thin
- moist
- semi permable membrane
What is the gas exchange surface in amoeba?
• cell membrane
Where does an amoeba organism live and where does the diffusion of gases occur?
• lives in water and it occurs over the whole of the body surface
Name some simple multicellular organisms?
- flatworms (aquatic animals)
* earthworms (terrestrial organism)
Why do simple multicellular animals have fairly small oxygen requirements?
- they are slow moving and so have a low metabolic rate
* O2/CO2 diffuse across the skin surface and do not have any special exchange organs
Features of a flatworm?
Structure : evolved to have a flattened shape
Function : increases S.A/volume ratio
Structure : no part of the body is far from surface
Function : short diffusion pathway
Features of earthworm?
Structure : very low metabolic rate
Function : not a lot of chemical rection happening in body
Structure : developed a tubular shape and restricted to damp environment of soil
Function : provides large S.A/V ratio compares to a compact organism of same volume
Structure : moist skin by secreting mucus onto surface
Function : allows gases to diffuse and dissolve
• once O2 is inside body, needs to be transported to internal cells - has a closed blood system containing blood within vessels.
Structure : Blood contains respiratory pigment
Function : transport of O2
• O2 diffuses into blood capillaries beneath skin surface/ carried in vessels to cells
Structure : circulatory system - CO2 transported in opposite direction to O2
Function : maintains a diffusion gradient at respiratory surface
What is gas exchange?
• the process by which oxygen reaches cells and carbon dioxide is removed from them.
Why do larger and advanced multicellular animals have a high metabolic rate?
• they need more energy and have a high requirement for oxygen
Name some advanced multicellular organisms?
- reptiles
- insects
- mammals
- fish
Why do multicellular organisms require a specialised gas exchange surface?
- to compensate for increases O2 demands
• small S.A/V ratio
• high metabolic rate
• diffusion distances are too large
• so diffusion can take place more rapid and efficiently
What additional features increase efficiency of gas exchange in organism that posses a circulatory system/respiratory pigment?
- an internal transport system : provided by blood circulation system to move gases between respiring cells and respiratory surface
- a respiratory pigment : located in the blood to increase the O2 carrying capacity of the blood
Why have animals evolved to have specialised gas exchange surfaces?
• so diffusion of gases in/out cells can take place rapidly and efficiently
What are the gas exchange surfaces?
- gills in fish
- alveoli in the lung of a mammal
- trachea in insects
What organisms are amphibians?
- frogs
- toads
- tadpoles
- salamanders
What is the gas exchange for the amphibians?
• the tadpoles live in water and have gills for gas exchange
Gas exchange in adults ; When inactive (rest) = through skin When active (mating) = through lungs
Give two functions of reptile ribs?
- protect and support organs in body
* help with ventilation of lungs
How does the structure of a reptile lung differ from amphibians lung?
• a complex internal structure because of in growth of tissues increasing S.A for gas exchange
The respiratory system of a bird?
- ventilation assisted by a system of air sacs connected to the lungs
- air sacs function as bellows. In birds, breathing in fills the lungs with completely fresh air.
- air passes through birds respiratory system in one direction, bringing fresh air into posterior air sacs and then into lungs.
- air flows into anterior sacs before it exists through trachea
What brings about movement of the muscles?
• ventilation
Why do birds need large volumes of oxygen?
To release ATP in flight muscles for respiration so a high oxygen demand
During flight the action of flight muscles ventilates the lungs
• air flow in birds is unidirectional so only oxygenated air comes in contact with the gas exchange surface
–> makes gas exchange more efficient
Advantage of bird lungs?
• no residual air left in lungs - lung always ventilated with fresh air
Respiratory system of insects?
- air diffuses into the insects through holes called spiracles running along each side of the body
- spiracles lead to a system of branched chitin lined air tubes called tracheae.
- the spiracles open and close like valves –> important bc it allows gas exchange and reduces water loss
Resting insects rely on diffusion
During periods of activity abdomen ventilate the tracheae; The end of the tracheael branches are called tracheoles; here gas exchange takes place which passes O2 directly in cells
In order to survive on land?
• terrestrial organisms need to conserve water but at same time the gas exchange surfaces need to be moist so efficient diffusion takes place
–> therefore organs of gas exchange need to be retained in the body
• prevents heat loss
• protection by the ribs or chitin exoskeleton in insects
What problems are caused by living in water?
- water contains less O2 than air
- rate of diffusion is slower
- water is a more dense medium than air and does not flow freely
How do fish overcome problem of living in water?
- Gill surface is thin
* have an extensive blood supply : O2/CO2 are exchanged into capillaries close to the epithelial cells of gills
Ventilation mechanism in fish?
- water flows in through the mouth, operculum is closed, the buccal cavity is lowers so
- the volume increases in cavity and the pressure decreases
As water flows out, the mouth is closed, the buccal cavity floor moves up, to increase the pressure , the volume decreases and water flows out through the open operculum
Structure of gills in bony fish?
- along each gill arch are thin lamellae and on these are gill plates
- the gill lamellae have a large surface area for gas exchange
- blood circulates through gill plates - O2 diffuses through gill plates into the capillaries and CO2 diffuses out into water
Counter current flow?
• e.g in bony fish
• blood flows through the gill capillaries in the OPPOSITE DIRECTION to water.
–> this ensures a diffusion gradient is maintained over the whole length of the gill plate ( blood always meets water with a higher oxygen content causing more efficient exchange of O2 from water into the blood for a long period of time )
• equilibrium is never reached
Parallel flow?
• e.g in sharks
• blood flows through the Gill capillaries in the SAME DIRECTION as the water flow
–> gas exchange is efficient at first- halfway across gill plate equilibrium is reached, no net diffusion of O2 from water into the blood
Ventilation of human lungs?
- during inspiration: external intercostal muscles contact, the ribs move up and out, the diaphragm contracts and flatterns, volume of thorax increases while pressure in thorax decreases and the outside air pressure is greater do air is drawn into the lungs
- during expiration the external intercostal muscles relax, the ribs move down and in, the diaphragm relaxes, volume in thorax decrease while pressure in thorax increase and the outside air pressure is lower so air moves out of the lungs
Gas exchange in alveoli are suitable because?
• walls of capillary/alveolus are one cell thick
- therefore short diffusion pathway
• moist surface
- for gases to dissolve
• large no. of alveoli
- large S.A for efficient diffusion
• each alveolus has a capillary network/blood circulates
- to maintain diffusion gradient for O2/CO2
What is a surfactant?
- chemical substance (phospholipid) which covers surface of alveoli.
- reduces surface tension and prevents alveoli from sticking together/collapsing when breathing out
Gas exchange in plants?
- leaves are thin
- large S.A
- air spaces in spongy mesophyll aid diffusion of gases through the leaf
- stomata in lower epidermis allow gases O2/CO2 to diffuse in/out
How are leaves adapted to photosynthesis?
• large S.A
- maximum light absorption
• can its orientate towards sun
- perpendicular at right angles to light source
• thin
- allow light to penetrate lower layers
•intercellular air spaces allow CO2 to diffuse into cells, O2 and water vapour to diffuse away
• cuticle and epidermis are transparent
• palisade cells are elongated and densely packed together and contain many chloroplasts
- chloroplasts can rotate and move within the mesophyll
Why do different mechanisms need ventilation?
- to supply the respiratory surfaces with a fresh supply of oxygen and to maintain diffusion gradients.
- the function of a ventilation mechanism is to move the respiratory medium, air or water, over the respiratory surface.
Why do gills not function effectively on land?
- because they dry out
* clump together because of surface tension
Why is counter current flow more efficient than parallel flow?
•it results in a higher O2 saturation
Gas exchange?
• the process by which oxygen reaches cells and CO2 is removed from them
